Information display illumination for direct or backlighting purposes is well known to those skilled in the art. Conventional information display devices such as a liquid crystal display require the presence of a light source in order to provide contrast which makes the display readable. When in high ambient lighting conditions such as sunlight, the liquid crystal display requires no additional illumination source in order to provide sufficient contrast.
However, in low ambient lighting conditions, display illumination is accomplished in conventional information display devices by the use of incandescent bulbs or electroluminescent display panels. Incandescent bulbs, when used as a means for display backlighting, yield significant undesirable bright spots in the areas of the display near their physical locations. Many attempts have been made to uniformly diffuse the light emitted from incandescent sources to provide a more consistent illumination of the information display area. The present trend in electronic information display devices is to use electroluminescent display panels as backlighting devices. When used as a backlighting illumination device, the electroluminescent display panel solves the problems of bright spots associated with the use of incandescent bulbs as backlighting devices. With electroluminescent display panels, designers now have an excellent means of providing a uniform illumination for backlighting a liquid crystal display when viewed in low ambient lighting conditions.
However, electroluminescent display panels are not without their problems. The most significant problem facing the design engineer after selecting the electroluminescent display panel for illumination of an information display is the high drive voltage required to effectively illuminate an electroluminescent display panel. Typical electroluminescent display panels require from 90 to 140 volts peak to peak applied across the electrodes of the display panel. In a portable device having an information display, conventional low power bipolar technologies used in most present integrated circuits are not capable of efficiently producing voltages in the ranges in the ranges mentioned from a single 1.5 volt energy source.
Thus, what is needed is a BIMOS circuit capable of generating the required drive voltage for an electroluminescent display panel from a low voltage, preferably a single cell having a DC voltage of approximately 1.5 volts.